1. Field of the Invention
This invention relates generally to an ablation apparatus for the selective ablation of the inner layers of body organs or lumens, and more particularly, to an ablation apparatus which includes an expandable member housing a heated electrolytic solution
2. Description of Related Art
There are a number of body organs and lumens, including but not limited to the uterus, gall bladder, large intestine and the like, that have inner layers which have abnormal conditions. Traditional methods of treatment have included removal of the body organ to treat the abnormal condition, the use of lasers, and the application of a thermal source.
A diseased condition of the uterus, menorrhagia, is defined as excessive menstrual bleeding in the absence of organic pathology. It has no known aetiology and it has been postulated that it is due to an inappropriate exposure of the endometrium to hormones. Menorrhagia is an exceedingly common problem, typically comprising approximately one in five outpatient referrals to gynecological departments. Women suffering severe menorrhagia are at risk from chronic anemia. The first treatment employed may be the administration of drug therapy. A major disadvantage is the need to administer drugs long term, and frequently the beneficial effects are only temporary. Another treatment is hysterectomy.
A number of physical and chemical methods have been tried as alternatives to hysterectomy, including the use of superheated steam, cryotherapy, urea injection and radium packing. The most commonly used methods as an alternative to hysterectomy are, ablation of the endometrium either by using a laser, such as a Nd:YAG laser, or the use of RF energy applied with an electrode.
Laser treatments have provided only limited success. RF is an attractive alternative. In RF heating, a conductive probe is placed within the uterine cavity and an insulated ground-plane electrode or belt is placed around the patient's midriff. RF energy is applied to the thermal probe with the external belt electrode acting as the return arm of the circuit. The electrical load presented by the RF thermal probe, patient, and external belt is matched to the output of the RF generator via a tuning unit, to form a series resonant circuit. Once tuned, the majority of the power applied to the probe is deposited into the endometrium as heat.
Current flows primarily capacitively, and an electric field is set up around the active tip of the probe. Tissue lying within the field becomes heated because of rapid oscillation of charged particles and locally induced currents.
Prior et al. have reported on the use of RF to treat menorrhagia. Power at 27.multidot.12 MHz was delivered to a probe that was placed into the uterine cavity and capacitively coupled to a second electrode consisting of a belt placed around the patient, Prior et al., Int. J. Hyperthermia, 1991, Vol. 7, No. 2, pgs 213 to 220. The active electrode was a 10 mm diameter stainless-steel cylinder with a length of 70 mm. This method, however, did not adequately deliver RF energy to the entire endometrium. Because the endometrium has an irregular surface, it is difficult to deliver sufficient RF energy to the entire structure and effectively treat menorrhagia.
However, it is desirable to have close contact between the RF conductive face and the endometrium. In U.S. Pat. No. 5,277,201 (the"'201 patent") an electroconductive, expandable balloon expands the interior of the uterus and effects electrical contact with the endometrial lining to be destroyed. The device of the '201 patent fails, however, to provide sufficient physical contact with the entire endometrium, and thus the treatment is not complete. Not only is the physical contact with the endometrium unsatisfactory, but the effective delivery of RF energy to the endometrium could be improved.
There is a need for an RF ablation apparatus, with an open foam cell structure surrounding an expandable member, that includes zones of semi-trapped electrolytic solution adjacent to electrodes, with a zone porosity that is less than non-zone sections of the open foam cell foam where there aren't electrodes. Additionally, there is a need for an ablation device which provides a heated electrolytic solution in the expandable member that is delivered to the inner layer of a body organ or lumen.